Superheterodyne radio receiver



Jan. 15, 1952 DAMMERS 2,582,683

SUPERHETERODYNE RADIO RECEIVER Filed Feb. 15 1950 INVENTOR. BERNHARDUSGERHARD'US DAMMERS AG ENT Patented Jan. 15, 1952 Bqrnha'rhus fGerhar'dusDam'mers, JEin'dhoven, Netherlands, assignor to Hartford National Bankand Trust Compa trustee hpelieatiofii bruary 15, 1950, Serial No;144,305

In the Netherlands F bruary 16,1949

The present invention relates to a 'suo dyne receiverja nd moreparticularl y to *a mixin'g circuit arrangement wherein both I the localI oscillations and the input signals are applied between the cathode'and the grid of the mixin'g tube.

For frequency transformation of ultra-short waves a diode is "generallyused. This, however, has the disadvantage that 'an additional tube isrequired for generating the local oscillations.

It is known to use a triode as an oscillatormodulatorf but 'thes'e knowncircuit-arrangementsare, as a rule, unsuitable for frequencytransformation of ultra-short "waves. H

'1he principle object of the present invention to provide a mixingcircuit-arrangement for the reception of ultra-short waves, of the typereferred to in the preamble, in which stable oscillator operation isensured and in which a high conversion conductance is achieved.

Another object of the invention is to provide a mixing circuit whereinlocal oscillations are not radiated by the antenna and in which afavourable signal-to-noise ratio is achieved.

Further objects of the invention will appear from the followingdescription.

According to the invention, the mixing circuit includes a discharge tubehaving a cathode, a control grid and an anode. An impedance network,from which the intermediate-frequency oscillations are derived, iscoupled between the anode and the grid. Connected in series with thisimpedance network is an impedance element across which the localoscillations occur and which is inductively coupled with an impedanceconnected between the cathode'and the grid, so that the localoscillations are produced in the tube itself and are applied, togetherwith the input signals, between the cathode and the grid of the tube.

The grid is preferably connected to a point of constant potential, suchas ground, and acts as a static screen between the cathode and theanode. It is to be noted that such so-called grounded-grid arrangementsfor amplifying ultra-high-frequency oscillations are often used when itis desired to amplify a comparatively wide frequency band. In mixingcircuits it is also known to connect the cathode, through an impedanceacross which the local oscillations occur, to a point of constantpotential and to supply the signal voltage to the grid. In such anarrangement, however, the output circuit is generally connected betweenthe anode and the point of constant potential, so that the grid does notconstitute a static screen beween the output circuit and the in utcircuit at the -'tiib e'-' a d-tne arrangement is not well suited forfrequency transformation of ultra-short waves. Q

According to the invention, there is interposed between the point'ofconstantpotential, towhi'ch the grid is "connected, and the anodearteries connection of a circuit tuned to "theiocal-qs" i latorfrequency and the impedancefid" the intermediate-frequency os'c'illati arived-i The inductance of the said o cut ductively coupled withaninducto'n' one-amd- -oi which is connected to the cathodepf the tubeand the-'other end of whichisc'onnected,: through a condenser, to thepoint of constant potential. The input signal is :fed to "a tapping onthe iwducto r, preferably to f'a 'c'enter tapping. I

In order that the invention may be more clearly understood and readilycarried into effect, it will now be described more fully with referenceto the accompanying drawing, in which one embodiment thereof is shown byway of-example.

Referring now to the drawing, the antenna circuit inductance l iscoupled with the inductance of a first circuit 2, which is tuned to thedesired signal frequency. The high-frequency oscillations developedacross this circuit are applied through filters 3 and 4, the purpose ofwhich will be explained hereinafter, and part of a feed-back coil 6, toa cathode 8 of a triode l. A grid 9 of triode I is grounded, withrespect to high-frequency oscillations, through a parallelconnection IIof a resistance and a condenser. An anode I0 is connected, through acircuit l2, which is tuned to the intermediate frequency, and a circuitI4 which is tuned to the oscillator frequency, to the positive terminalof the supply. The circuit I2 is coupled with a circuit l3, which isalso tuned to the intermediate frequency, and from which theintermediate-frequency oscilla tions are derived for furtheramplification and detection.

As a triode, it is advantageous to employ a so called disc-seal tube ora grounded-grid triode, in which the grid constitutes an eifectivestatic screen between the anode and the cathode and is grounded for thispurpose. In the latter, the grid is provided with a number of supplyleads in order to reduce the inductance.

The inductance of circuit I 4 is inductively coupled to coil 6 so thatthe triode operates as an oscillator and local oscillations occur acrossthe circuit l4. If the antenna circuit is connected to the centre ofcoil 6 and a condenser I5 is connected between the lower end of thiscoil and ground, and if condenser I5 is chosen to be approximately equalto the grid-cathode capacity, local oscillations will not occur acrossthe antenna circuit 2 and troublesome radiation will not take place. Aresistance 11, connected in parallel with condenser I5, is chosen to beapproximately equal to the input resistance of the tube. Aparallel-connection of a resistance and a capacity coupled between thetap on coil 6 and ground serves to apply a suitable positive bias to thecathode 8. This resistance is traversed by the cathode current. Aninductance l6, interposed between the tap on coil 6 and circuit 6,serves to prevent the high-frequency signal currents from flowing toground. The filters 3 and 4 included in the lead between the antennacircuit-fiend the tap on coil 6 serve to keep the antenna circuitisolated from the intermediatefrequency oscillations and the localoscillator oscillations respectively. The filter 4 thus amplie V fiesthe effect of the balanced bridge-circuit formed by the two parts ofcoil 6, condenser l5 and the grid-cathode capacity of the tube.

While I have described my invention in a specific use thereof and in aspecific embodiment, I do not wish to be limited thereto, for obviousmodifications will occur to those skilled in the art without departingfrom the spirit and scope of 4 said intermediate frequency wave and saidsec-- and wave and coupled in series between said anode and groundpotential, said second impedance network including an inductance, meansto derive said intermediate frequency wave from said first impedancenetwork, a third impedance network having a low impedance at thefrequencies of said first and second waves interposed between saidcontrol grid and ground potential, a tapped inductive element having oneend thereof coupled to said cathode and having the other end thereofcoupled to ground potential, said inductive element and said secondimpedance network being inductively coupled to apply said second wave tosaid control grid-cathode circuit in positive feedback relationship, andmeans to apply said first wave to the tap on said inductive element.

2. A mixing circuit arrangement, as set forth in claim 1, furtherincluding a resistance capacitance parallel network interposed betweensaid other end of said inductance element and ground potential to applya positive bias to said cathode.

BERNHARDUS GERHARDUS DAMMERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Mountjoy Aug. 4, 1936

